DC Circuit Breaker Interrupting Ratings - Ungrounded vs End-Grounded

[PracticalQuixotism]

I am exploring options to improve the interrupting rating of a particular circuit breaker in an ungrounded 125VDC system. The breaker in question has an interrupting rating of 10000A at 125VDC. The breaker has 3 poles, but only 2 poles are currently being utilized (1 pole for the positive leg and 1 pole for the negative leg).

I have located a vendor document that states that for a 2-pole configuration the interrupting rating is 14000A at 250VDC. The document provides the following details:

"Multi-pole ratings (2 or 3) are based on midpoint grounded systems with one pole in positive leg and one pole in negative leg, or end grounded systems with two or three poles wired in series in the ungrounded leg."

With respect to the breaker interrupting rating, what is the distinction between an ungrounded system and an end-grounded system? Would I be able to wire 2 poles in series in the positive leg of my ungrounded system and take credit for the 14000A interrupting rating? Also, if a breaker has an interrupting rating of 14000A at 250VDC, is it safe to assume that it is capable of interrupting 14000A at 125VDC?

 

[TurbineGen]

Answering your second question: Yes it is safe to assume that if a breaker is rated for 14KA at 250 VDC, that is will break 14KA at 125VDC.

I'm unsure about your other question, but my gut feeling is no. If the breaker is designed to break 14KA at 250 VDC with just a single interrupter, then you could parallel them to obtain a higher breaking current. However it sounds like this unit requires 2 interrupters in series for DC and thus paralleling two and then placing one in series would not suffice.

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